Check the obvious first, Sea Strainer and hoses. It sounds like you are back at the dock
, so check water flow at the exhuast.
The less obivous are the impeller, which will sometimes fail at less than 200 hours and the heat exchanger
, which could be getting some growth inside it, resisticting water flow at higher RPMs
With that said, if you were motoring into heavy seas, towing a dinghy
, at high RPMs for that egnine, you probabaly over heated it from the drag on the boat.
I think the Max RPMs on that engine is 3200? So normally you would run no more than 80% of max RPM or about 2560 rpm.